read_project can be prevented by a very expensive condition, which we want to
avoid, while still not writing manual SQL queries. read_project_for_iids is used
by read_issue_iid and read_merge_request_iid to satisfy both of those
constraints, and allow the declarative policy runner to use its normal caching
strategy.
This class can be used to reduce a list of issues down to a subset based
on user permissions. This class operates in such a way that it can
reduce issues using as few queries as possible, if any at all.
